The present invention relates in general to automotive noise cancellation, and, more specifically, to reducing unheard, ultrasonic sound energy impinging on vehicle occupants.
With the increasing development of driver-assistance and autonomous features, modern vehicles are accumulating a large suite of sensors to monitor and measure the driving environment. Ultrasonic sensors, which measure short-range distance using radiated ultrasonic sound waves, are inexpensive additions to an assortment of sensors typically used in passenger vehicles. They are used to augment or add redundancy to features such as parking assist, collision avoidance, and adaptive cruise control.
Ultrasonic sound energy is inaudible to passengers since it is beyond the range of human hearing. Direct application of ultrasound to the human body (e.g., as in ultrasonic imaging) is being studied for its biological effects. In the context of factory/working environments, some jurisdictions have adopted exposure limits due to potential complaints of nausea, headaches, dizziness, confusion, and stomach pain from workers using drills, welding tools, or other industrial equipment which can generate ultrasound at high volume levels. Although incidental exposure to ultrasound generated by automotive sensors does not present health risks, it may nevertheless be desirable to reduce exposure. For example, there may be potential effects on sensitive electronics brought by a passenger into the vehicle or being used by nearby persons (e.g., pedestrians) or in other vehicles. It may also be desirable to consider the potential impact on nearby animals like bats or insects, some of which depend on ultrasonic sound ranges for mating, prey, communication, and navigation.
Audible cabin noises have previously been addressed using Active Noise Cancellation (ANC) systems. Road, wind, and engine noises are reduced in order to provide a quieter passenger environment by injecting inverse or anti-noise into the passenger cabin using vehicle-mounted loudspeakers. ANC works by measuring an acoustic signal and then performing delay and phase inversion calculations for one or more speakers to output a cancelling signal, so that both sound fields reach the occupant's ear at the same time. Most ANC systems in conventional vehicles focus on cancelling very low frequency noises like those from engine idle or body “boom” noises because the corresponding low frequency wavelengths make the anti-noise easier to calculate and easier to produce. ANC systems have not been capable of addressing inaudible (e.g., ultrasonic) sound energy in passenger cabins.